The goal of the work is to understand the role of steroid hormones in control of tumor cell growth in culture. Most of the work will be done with cells derived from an estrogen- dependent kidney tumor induced in hamsters. Initially, the problem lends itself to a division into two broad areas: 1. Development of clonal cell lines which depend for growth upon the presence of the appropriate steroid hormones. 2. Investigations of the effect of steroid hormones on control of cell cycle traverse, and on tumorigenesis. The primary emphasis of this project will be development of cell selection techniques useful for establishing clonal lines of estrogen- dependent kidney cells in culture.